Advancements in turbomachinery performance have been linked to turbine inlet temperatures that can be reliably sustained during service. Increases in efficiency through this method typically produces a hotter operating environment for turbine flow path components and hardware in which the working fluid is several hundreds of degrees higher than the melting point of component alloys. In one example, to protect components while operating in these high temperature environments, dedicated cooling air is extracted from a compressor section and is used to cool gas path components in a turbine section, such as rotating blades and stator vanes for example, incurring significant cycle penalties.
One method of cooling extremely high temperature applications utilizes film cooling in combination with backside convection. This method uses cooling air delivered internally of the component to emit from cooling holes a cooling flow over an external surface of the component which then results in a reduction of local external surface temperatures at downstream locations. These cooling holes are typically formed using an Electrical Discharge Machining (EDM) or laser drilling process. These processes typically form straight line holes that have round or diffuser shaped openings.
One location that is difficult to effectively cool is any filleted region that connects one portion of a component to another portion. For example, the curved region that connects an airfoil to inner and outer flowpath endwalls is extremely difficult to cool. This interface is highly, mechanically loaded and therefore must have very large fillet radii to reduce stress concentrations. Various methods have ineffectively been used to cool this area. Examples of such methods include using internal holes to cool the area which can further increase stress concentrations, and forming cooling hole exits on the endwall itself and then directing cooling flow toward the fillet which is highly inefficient.